The invention is directed to ceramic products made from fiber glass waste; raw batch formulations for making ceramic products from fiber glass waste; and a method for making ceramic products from fiber glass waste. Examples of ceramic products that can be made by the invention are tile and brick, but other ceramic products can also be made. The invention addresses two current problems: energy usage by the ceramic industry needs to be reduced; and new technology is needed to reprocess fiber glass waste into useful products.
The ceramic industry consumes large amounts of energy, especially during the firing process. Firing temperatures greater than 1200° C. (2200° F.) are required to sinter typical ceramic raw materials into dense products. Modifications of the raw material formulations have led to reductions in firing temperatures, but the improvements are limited because of the types of raw materials used. Most traditional ceramic products, such as tile and brick, consist mainly of clay-based raw materials, which inherently require high firing temperatures. Other ceramic manufacturing steps, such as the drying processes, are also very energy intensive. Energy costs are a major portion of the total manufacturing costs, and thus new methods to reduce the amount of energy required will be a great benefit to the ceramic industry.
The fiber glass industry produces large amounts of fiber glass waste that currently can not be economically recycled, and thus is disposed of in landfills. Fiber glass waste is generated during the fiber forming process, and also during the manufacture of fiber glass products. Fiber glass wastes are potentially recyclable by remelting to form new glass fibers. However, fiber glass waste is generally not remelted, because impurities in the waste lead to unacceptable levels of fiber breakage during the forming process. Recycled glass, referred to as cullet, is commonly used as 20-35% of the raw materials in the manufacture of many types of glass products. Cullet is also used in some types of fiber glass manufacturing, but is mainly from container and flat glass sources.
The two main types of fiber glass are wool for insulation products, and continuous fibers for textile products. Fiber glass wool is formed by rapidly spinning molten glass through holes in a rotating cylindrical container. Continuous glass fibers are formed by drawing molten glass through precious metal bushings. In both methods the fibers are rapidly cooled by air or steam blowers. An organic chemical treatment of size is then applied to minimize fiber-to-fiber abrasion during processing, and to provide coatings necessary for the particular product application.
During processing various malfunctions periodically occur, such as fiber breakage, which result in waste material. The coating of size on the fibers prevents immediate reuse of the waste as cullet, because the size causes unacceptable amounts of residual carbon to form in the melt. Additional processing steps can be used to remove the size prior to melting, but this additional processing is not economical compared to the use of raw batch materials. Studies further indicate that even when the size is removed, other contaminants are present which result in high rates of fiber breakage during forming. Because of these problems, large volumes of fiber glass waste are currently disposed of in landfills. New technology is needed to reprocess this industrial waste into useful products.
Waste glass in the invention refers to any industrial or post-consumer fiber glass that is discarded. Any form of fiber glass, such as continuous fibers for textile products or wool for insulation products, can be used. In addition, any other forms of waste glass from fiber glass melting processes, such as drain glass, can also be used in the invention. Fiber glass waste can be obtained from fiber glass manufacturers, but other sources of fiber glass can also be used. There are various types of fiber glass compositions designed for a wide range of applications. Fiber glass compositions typically soften from about 650 to about 800° C. This unique softening behavior causes articles formed from fine powders of fiber glass to densify by viscous-phase sintering at temperatures much lower than usually required to fire ceramic products. The invention utilizes the low-temperature densification behavior of fiber glass to reduce manufacturing costs by conserving energy and lowering equipment and maintenance expenses.
The invention is novel, because a high-quality ceramic product can be manufactured at low cost from up to 100% fiber glass waste. The invention conserves energy and natural resources compared to traditional ceramic processing methods. An impervious ceramic microstructure with only a small amount of porosity can be achieved. Impervious refers to ceramic products with very low water absorptions of less than 0.5%. An impervious ceramic microstructure with a small amount of porosity is critical to achieve high-quality properties. Ceramic products can be produced by the invention with a wide range of colors with smooth glossy glaze-like surfaces. The surface texture and other fired properties can also be adjusted by the addition of fillers, and/or by partial crystallization of the glass.
Previous methods have been developed to produce ceramic products from waste glass. U.S. Pat. No. 6,340,650 reviews processing problems that result from previous methods, and provides a method to eliminate these problems by avoiding the use of water and clay in the processing. There are several types of fiber glass compositions. These compositions are designed to be less susceptible to chemical reaction with water compared to container and flat glass compositions, because of the large surface area of fiber glass. Less sensitivity to reaction with water allows greater flexibility in processing of fiber glass compared to container or flat glass. In addition, some fiber glass compositions, such as E-glass, have higher softening temperatures compared to container and flat glass compositions. The higher softening temperature allows clay and other ceramic raw materials that produce volatile species during firing to be included in the raw batch formulation without adversely affecting the densification behavior. The present invention provides a method of making ceramic products from fiber glass waste where water and clay can be added during processing.
It was also unexpected that the use of fiber glass would provide several other significant advantages compared to the use of container or flat glass. This is because of differences in composition and contaminants, but especially because of the different forms of glass (fibers versus bulk glass). Processing container or flat glass into a fine powder involves two or three energy-intensive crushing and grinding steps. Glass fibers are typically 3-100 micrometers in diameter, and thus only one dimension needs to be broken to produce very fine powder. Chopping or milling of fiber glass is much simpler and less energy intensive compared to crushing container or flat glass. Industrial sources of fiber glass waste are very uniform in composition with much less contamination compared to post consumer container glass. This allows more control over color and other properties of the ceramic product produced. In addition, the significantly lower thermal expansion coefficients of fiber glass compositions compared to container and flat glass offers the possibility of improved thermal shock resistance.
The invention offers a variety of environmental benefits compared to current practices. The method completely transforms fiber glass into a dense ceramic product, so that all future environmental problems in the handling and disposal of the fibers is eliminated. By using recycled glass as the raw material; mining, processing, and transportation of traditional raw materials is not required. The invention requires substantially less energy compared to traditional clay-based tile production, and especially compared to glass-melting methods of producing tile. This is mainly because of greatly reduced firing temperatures of 700-1000° C., compared to 1200° C. for clay-based tile, and >1500° C. for melt-based tile.